Composite stamper for imprint lithography

ABSTRACT

A stamper having a patterned layer composed of a hard material and a compressible material back plane layer. The back plane layer may be composed of an elastomer. The stamper may be used to imprint an embossable layer disposed above a substrate for the production of a magnetic recording disk.

REFERENCE TO RELATED APPLICATION

This application is a divisional of Ser. No. 10/741,316 filed Dec. 19,2003.

TECHNICAL FIELD

Embodiments of this invention relate to the field of manufacturing and,more particularly, to stampers for imprint lithography.

BACKGROUND

Stamps are used in a variety of applications and for various purposes.Areas of stamp use include micro contact printing (μCP) and nanotransfer printing (nTP). Contact, or transfer, printing relies onsurface chemistries for transferring thin films from the raised regionsof a stamp to a substrate when these two elements are brought intophysical contact. This technique is an additive process utilizingpatterning approaches referred to as soft lithography. An articleentitled “Printing meets lithography: Soft approaches to high-resolutionpatterning,” by B. Michel et al., IBM J. Res. & Dev. Vol. 45 No. 5September 2001, describes the use of an elastomer stamp in micro contactprinting. The described elastomer stamp (a.k.a. hybrid printing stamp)is composed of a patterned elastomeric layer attached to a compressibleback plane of supporting material (such as a metal), as illustrated inFIG. 1A. The patterned elastomeric layer of the stamp is inked and thenprinted onto a hard substrate, forming a monolayer of ink on the hardsubstrate, as illustrated in FIG. 1B. Transfer printing utilizing such astamp is performed with the application of only a small pressure.

In contrast to contact printing, embossing is an imprinting process thatdisplaces or molds a layer of material with a stamper. The imprintingprocess requires a greater amount of applied pressure than with stampsused in contact printing. A trend in embossing is the development ofnano imprint lithography (NIL) techniques. NIL techniques are being usedin the disk drive industry to produce discrete track recording (DTR)magnetic disks. DTR disks typically have a series of concentric raisedareas (a.k.a. hills, lands, elevations, etc.) storing data and recessedareas (a.k.a. troughs, valleys, grooves, etc.) that provide inter-trackisolation to reduce noise. Such recessed areas may also store servoinformation. The recessed areas separate the raised areas to inhibit orprevent the unintended storage of data in the recessed areas.

NIL involves the use of a pre-embossed hard forming tool (a.k.a.stamper, embosser, etc.) having an inverse (negative replica) of a DTRpattern. The stamper is pressed onto a thin layer of polymer on a disksubstrate. The stamper and polymer/substrate may each be heated, coupledand then the stamper is removed leaving an imprint of the DTR pattern onthe polymer layer.

One requirement of an NIL technique in the production of DTR magneticdisks is the ability to produce sub 100 nanometer (nm) features in areliable way. In the imprinting process, the polymer thickness maytypically be in the range of 40 to 500 nm, which may be less than thethickness variation of a stamper and the polymer/substrate surface. NILrequires application of a stamper that allows for good compliance orparallelism between the polymer/substrate surface and the stampersurface. The compliance between the surfaces is limited by surfacemorphology of the imprinted surface and also by the thickness of thestamper. One problem with conventional NIL stampers, which are typicallyaround 300 microns thick, is that they may not provide for goodcompliance between the disk surface and the stamper surface due to theirthickness. While it is possible to increase compliance by reducing thethickness of the stamper, such an approach may not be acceptable since avery thin stamper would be difficult to handle during its formation(such as during a plating operation) and also during mounting of thestamper into a press system.

A problem with using the patterned elastomer layer printing stamps orhybrid printing stamps described above for imprinting operations is thatsuch stamps may not be sufficiently hard for embossing operations. Suchstamps may be too soft for generating sharp and fine grooves or othersimilar embossed structures that may be need for imprinting operationsand may not have sufficient durability for the large number of imprintsperformed in manufacturing. Such stamps may be limited to use in contactprinting operations that utilize low stamping pressure.

One patent, U.S. Pat. No. 6,517,995, describes the use of an elastomericstamp in a liquid embossing process. In such an embossing process, athin film of material is deposited on a substrate. The depositedmaterial is either originally present as a liquid or subsequentlyliquefied prior to embossing. The material is patterned by embossing ata low pressure using a patterned elastomeric stamper. The patternedliquid is then cured to form a functional layer. Such a stamper,however, may be limited to use only with a liquid embossing process thatutilizes a low stamping pressure and a liquid embossing substance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings in which:

FIG. 1A illustrates a prior stamp composed of a patterned elastomericlayer attached to a compressible back plane of supporting material.

FIG. 1B illustrates a contacting printing process that forms an inklayer on a hard substrate using the stamp of FIG. 1A.

FIGS. 2A-2E are cross sectional views illustrating one embodiment of thestructures of a composite stamper during its fabrication.

FIG. 3 illustrates one embodiment of a method of fabricating a compositestamper.

FIG. 4 illustrates one embodiment of an imprinting method using thecomposite stamper of FIG. 2E.

FIGS. 5A-5C are cross sectional views illustrating an alternativeembodiment of the structures of a composite stamper at different stagesof its fabrication.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forthsuch as example of specific materials or components in order to providea thorough understanding of the present invention. It will be apparent,however, to one skilled in the art that these specific details need notbe employed to practice the invention. In other instances, well knowncomponents or methods have not been described in detail in order toavoid unnecessarily obscuring the present invention.

The terms “above,” “on,” “below” as used herein refer to a relativeposition of one layer or component with respect to other layers orcomponents. As such, one layer or component above or on another layer orcomponent may be directly in contact with the other layer or component,or may have one or more intervening layers or components. Furthermore,one layer or component deposited or disposed between layers orcomponents may be directly in contact with the layers/components or mayhave one or more intervening layers/components.

It should be noted that the apparatus and methods discussed herein maybe used to fabricate various types of disks. In one embodiment, forexample, the apparatus and methods discussed herein may be used tofabricate a magnetic recording disk. Alternatively, the apparatus andmethods discussed herein may be used to fabricate other types of digitalrecording disks, for example, optical recording disks such as a compactdisc (CD) and a digital-versatile-disk (DVD). In yet other embodiments,the apparatus and methods discussed herein may be used in otherapplications, for example, the production of semiconductor devices, andliquid crystal display panels.

A composite stamper having a compressible back plane layer coupled to ahard material imprinting structure is described. The hard material mayalso be a rigid material. In one embodiment, the imprinting structure ofthe stamper may be formed by electroplating a mold with a hard material,for example, nickel (Ni) to produce a hard material patterned layer andthen disposing a polymerized layer of elastomer on the back plane (sideopposite that of the imprinting pattern) of the hard layer. The bondingof such an elastomer to the hard material patterned layer may allow foreasy handling of the stamper and may also assure a uniform pressuredistribution and good compliance during imprinting. In one embodiment,the patterned layer may be thin relative to a thicker elastomer layer.The stamper, or embossing tool, may be used to create a discrete trackpattern on an embossable layer material (e.g., deformable solid)disposed above a substrate for the production of a magnetic recordingdisk. Where the stamper is to be used for the imprinting of anembossable layer on a disk shaped substrate (e.g., a magnetic recordingdisk substrate), the stamper may have a corresponding disk shape. Insuch an embodiment, a dimension of the stamper may be referred to as adiameter. Alternatively, the stamper may be oversized and/or differentshaped relative to the size and shape of the substrate and/or embossablelayer to be imprinted. In alternative embodiments, the stamper may haveother shapes and other corresponding dimensions (e.g., widths andlengths).

The apparatus and methods discussed herein may enable the production of,for example, sub 100 nanometer (nm) features in an embossable layer in areliable manner. In the imprinting process, the embossable layerthickness may be, for example, in the range of 10 to 500 nm, which maybe less than the thickness variation of a stamper and the embossablelayer/substrate surface. The apparatus and methods discussed herein mayfacilitate good compliance or parallelism between an embossablelayer/substrate surface and a stamper surface. It should be noted thatalthough the apparatus and methods are discussed herein in relation tonano imprint lithography, the apparatus and methods may also be usedwith other scale (e.g., micro) imprint lithography techniques.

The following discussion is made in reference to FIGS. 2A-2E and FIG. 3that illustrate one embodiment of a method of producing a compositestamper and its structure. In one embodiment, a hard patterned layer 210of composite stamper 200 may be formed from a master template 110 ofFIG. 2A. The generation of a master template is known in the art;accordingly, a detailed description is not provided. For the discretetrack media, the shape of the master template 110 will end up being thedesired pattern to be embossed into an embossable layer (e.g., apolymer) of a magnetic recording disk. As such, the surface topographyof the master template 110 is used to generate the shape of thepatterned layer 210 that is the inverse of the pattern that will beembossed into the embossable layer of the magnetic recording disk. Thepatterned layer 210 may have, for example, shape features having alateral dimension less than approximately 100 nm. Alternatively,patterned layer 210 may have shaped features greater than 100 micron.

In one embodiment, a patterned layer 210 is generated by, for example,electroforming a hard material (e.g., Ni) on top of the master template110, step 310. The Ni metal alloy may be, for example, electroplatedonto the master template 110. In an alternative embodiment, NiP may beplated (e.g., via electro-deposition or electroless deposition) on themaster template 110. Alternatively, other hard metals or metal alloymaterials may be used for patterned layer 210, for example, chromium. Inone embodiment, for example, the hardness of the material for patternedlayer 210 may be approximately in the range of HV100 to HV1000 on theVickers hardness test and HK60 to HK1000 on the Knoop hardness test.Exemplary hardness values for various metals and metal alloys that maybe used are as follows: Ni˜HK550, Cr˜HK930, and NiP (afterplating)˜HK500-HK600. These hardness values are only exemplary and thesemetals/metal alloys may have other hardness values.

It should be noted that plating is one of several additive processesthat may be used to form patterned layer 210. Alternatively, otheradditive processes, for example, spin coating, dip coating, CVD andsputtering may be used. In alternative embodiments, subtractiveprocesses such as reactive ion etching (e.g., of quartz or Ni material)may be used.

Furthermore, other hard materials may also be used for the patternedlayer 210, for example, glass and ceramic. In one embodiment, afterformation, the patterned layer 210 may be separated from master 110.Alternatively, the patterned layer 210 may be separated from master 110at other stages, for example, after the back plane layer 220 is cured,as discussed below. The separated patterned layer 210 is illustrated inFIG. 2B. In one embodiment, the raised areas of the patterned layer 210may have an approximate height 213, for example, on the order of 0.1microns. Alternatively, the raised areas of the patterned layer 210 mayhave other heights.

Next, in one embodiment, a masking layer 217 may be applied to the backplane surface 215 of the patterned layer 210, step 330, as illustratedin FIG. 2C. The masking layer 217 enables the formation of outer wall onthe back plane surface 215 of the patterned layer, step 340, asillustrated in FIG. 2D. The masking layer 217 may be composed of variousmaterials, for example, a photoresist. Masking layers are known in theart; accordingly a detailed discussion is not provided. In oneembodiment, the outer wall 211 may be formed on the back plane surface215 of patterned layer 210, around masking layer 217, by plating.Alternatively, other methods may be used to generate outer wall 211. Theouter wall 211 may be of the same or different material than thematerial used for patterned layer 210. The use of outer wall 211 onstamper 200 may prevent the compressible material 220 from beingsqueezed laterally outwards during pressing of stamper 200 into anembossable material as discussed below in relation to FIG. 4.

Next, the masking layer 217 is removed, step 350, and then acompressible material 220 is disposed on the back plane surface 215 areaof the patterned layer 210 within the cavity formed by outer wall 211,step 360, as illustrated in FIG. 2E. The compressible back planematerial 220 may be generated in situ or, alternatively, applied usingother techniques. For example, the top surfaces of wall 211 may bemasked and then recessed area of surface 215 coated with a liquid thatis subsequently solidified. Alternatively, the patterned layer's backplane may be coated using other techniques, for example, chemical vapordeposition (CVD), and dip-coating or spin-coating where a very thin filmis to be used.

Next, the material of back plane layer 220 may be cured, step 370. Inone embodiment, curing may be performed by heating stamper 200 to exposethe back plane layer 220 to an elevated temperature for some duration.Heating may be performed to effect a strong attachment between backplane material and the hard material of patterned layer 210. In oneembodiment, the curing may be performed in approximately the range ofroom temperature to 150 degrees Centigrade (C) with the curing timebeing approximately in the range of 24 hours to 15 minutes,respectively. In other embodiments, other temperatures and curing timesmay be used. Alternatively, the material of back plane layer 220 may becured without heating, for example, by waiting a certain amount of timebefore use of stamper 200. If not already separate, the patterned layer210 may be separated from master 110, step 380.

In one embodiment, the compressible back plane layer 220 may be composedof a silicon elastomer, for example, Sylgard 184™ available from DowCorning Corporation of Michigan. Alternatively, other types ofelastomers, for example, urethanes can be used. The elastomer used forcompressible back plane layer 220 may have a hardness value, forexample, in the approximate range of 20 to 55 on the Shore 00 scale andbetween 10 and 100 on the Shore A scale. Alternatively, othercompressible materials of other hardness values may be used. It shouldbe noted that although layer 220 may be discussed, at times, in relationto an elastomer, other types of materials, such as a UV curable material(with such material, correspondingly, UV cured in step 370) may be usedfor compressible back plane layer 220. Yet other thermosetting orradiation setting materials may be used for back plane layer 220. Theparticular material selected for use as compressible back plane layer220 may be based on various factors including, for example, its thermalresistance, hardness, adhesion to the patterned layer material andresilience to repeated pressure events.

In one embodiment, the thickness 222 of the back plane layer 220 may beapproximately equal to or greater than the thickness 212 of thepatterned layer 210. For example, the thickness 212 of the patternedlayer 210 may be approximately in the range of 1 to 100 microns and thethickness 222 of the back plane layer 220 may be approximately in therange of 100 microns to 5 millimeters. The use of a thin patterned layer210 with a thickness equal to or greater than the thickness ofcompressible (e.g., elastomer material) back plane layer 220 may allowfor easy handling of stamper 200 and may assure a more uniform pressuredistribution and good compliance during imprinting of an embossablelayer, as illustrated in FIG. 4.

FIG. 4 illustrates one embodiment of an imprinting method using thecomposite stamper of FIG. 2E. A base structure 400, having an embossablelayer 410 disposed thereon, is placed in a nest 430. In one embodiment,embossable layer 410 may be a deformable solid. In one embodiment,substrate 400 may be a substrate used for a magnetic recording disk. Insuch an embodiment, stamper 200 may be used for the imprinting ofembossable layer 410 for the production of magnetic recording disks. Themagnetic recording disk may be, for example, a discrete tracklongitudinal magnetic recording disk having, for example, anickel-phosphorous (NiP) plated substrate as a base structure 400.Alternatively, the magnetic recording disk may be a discrete trackperpendicular magnetic recording disk having a soft magnetic filmdisposed above a substrate for the base structure 400. In the embodimentwhere base structure 400 is disk shaped, nest 430 may be an annular ringhaving approximately the same thickness as the embossable layer 410/basestructure 400 for securing the base structure 400. In embodiments wherebase structure has other shapes (e.g., square, rectangular, etc.) nest400 may be similarly shaped to secure the base structure. Such a nest400 may prevent the stamper 200 from wrapping around the edge ofembossable layer 410/base structure 400 and facilitate greatercompliance near the outer edge of embossable layer 410.

After base structure 400 is positioned in nest 430, stamper 200 may bepositioned and aligned over the base structure. Stamper 400 is broughtinto contact with embossable layer 410 and a press 440 is used to applypressure to stamper 200 in order to imprint the embossable layer 410with the patterned layer 210. In one embodiment, for example, thepressure applied to the stamper 200 may be approximately in the range of10 to 2,000 psi. Alternatively, other pressures may be used. In oneembodiment, the diameter of the press 440 may be approximately the sameas the diameter 421 of the back plane layer 220. Alternatively thediameter of the press 440 may be less than or greater than the diameter421 of the back plane layer 220. In one embodiment, the embossable layer410 thickness may be, for example, in approximately the range of 40 to500 nm, which may be less than the thickness variation of stamper 200and the embossable layer 410/base structure 400 surface.

In the illustrated embodiment of FIG. 4, only a single side of basestructure 400 having embossable layer 410 is imprinted. In such anembodiment, block 440 may represent a hard, flat planar surface.Alternatively, imprinting may be performed simultaneously on embossablelayers residing on both sides of base structure 400. In such anembodiment, block 440 represents a stamper and press for imprinting anembossable layer on that side of base structure 440.

In another embodiment, the diameter 421 of the back plane layer 220 maybe approximately equal to or greater than the diameter 411 of the areaof the embossable layer 410 to be imprinted by the patterned layer 210.Alternatively, the diameter 421 of the back plane layer 220 may be lessthan the diameter 411 of the area of the embossable layer 410 to beimprinted by the patterned layer 210.

In one embodiment, a release layer (not shown) may be disposed on thepatterned layer 210 of stamper 200 and/or the embossable layer 410before imprinting to facilitate separation of the stamper 200 from theembossable layer 410 after imprint.

FIGS. 5A-5C illustrate an alternative embodiment of a method ofproducing a composite stamper and its structure. Patterned layer 210 ofFIG. 5A may be formed in a manner similar to that discussed above withrespect to FIGS. 2A and 2B. In this embodiment, a side wall 511 may beadded around the edge of patterned layer 210, forming a cavity above theentire back plane surface 215 area of layer 210. A compressible material220 is disposed on the entire back plane surface 215 of the patternedlayer 210 within the side wall 511, as illustrated in FIG. 5B. Thecompressible back plane layer 220 may be generated in a manner similarto that discussed above with respect to FIG. 2E. The side wall 511 maythen be removed to produce a stamper 200 having compressible back planelayer 220 dispose along the entire diameter 515 of stamper 200, asillustrated in FIG. 5C.

It should be noted that the patterned layer 210 has been shown withraised structures across most of its diameter for illustrative purposesonly. The patterned layer 210 may have an imprinting structure alongonly certain portions of its diameter, or other dimension. For example,patterned layer 210 may be structured to provide an imprinting structurefor an area of the embossable layer 410 residing above a portion of thebase structure 400 to be used for a data zone of a magnetic recordingdisk while having no imprinting structure, or a different imprintingstructure (e.g., different raised area to recesses area ratio), for anarea of the embossable layer 410 residing above a portion of the basestructure 400 to be used for a landing zone and/or a transition zone. Itshould also be noted that the ratio of the raised areas to recessedareas of patterned layer 210 need not be uniform across the patternedlayer 210.

As previously noted, the apparatus and methods discussed herein may beused with various types of base structures (e.g., wafer and paneloxide/substrates) having an embossable layer disposed thereon. In analternative embodiment, for example, the imprinting apparatus andmethods discussed herein may be used to fabricate semiconductor devicessuch as, for example, a transistor. In such a fabrication, an embossablelayer may be disposed above a base structure of, for example, an oxide(e.g., SiO₂) layer on top of a silicon wafer substrate. A stamper may begenerated with a patterned structure for active areas of the transistor.The stamper is imprinted into the embossable layer with the embossedpattern transferred into the oxide layer using etching techniques (e.g.,reactive ion etching). Subsequent semiconductor wafer fabricationtechniques well known in the art are used to produce the transistor.

In an alternative embodiment, for example, the imprinting apparatus andmethods discussed herein may be used to fabricate pixel arrays for flatpanel displays. In such a fabrication, an embossable layer may bedisposed above a base structure of, for example, an indium tin oxide(ITO) layer on top of a substrate. The stamper is generated with apatterned layer being an inverse of the pixel array pattern. The stamperis imprinted into the embossable layer with the embossed patterntransferred into the ITO using etching techniques to pattern the ITOlayer. As a result, each pixel of the array is separated by an absenceof ITO material (removed by the etching) on the otherwise continuous ITOanode. Subsequent fabrication techniques well known in the art are usedto produce the pixel array.

In yet another embodiment, as another example, the imprinting apparatusand methods discussed herein may be used to fabricate lasers. In such afabrication, embossable material areas patterned by the stamper are usedas a mask to define laser cavities for light emitting materials.Subsequent fabrication techniques well known in the art are used toproduce the laser. In yet other embodiments, the apparatus and methodsdiscussed herein may be used in other applications, for example, thefabrication of multiple layer electronic packaging and opticalcommunication devices, and contact/transfer printing.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and figures are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

1. A method, comprising: providing a stamper, the stamper comprising: a patterned layer comprising a hard material, the patterned layer having a back plane; and a back plane layer directly bonded to the back plane of the patterned layer, the back plane layer comprising a compressible material; and imprinting the patterned layer into an embossable layer, the embossable layer being disposed above a substrate.
 2. The method of claim 1, wherein the hard material comprises a rigid material.
 3. The method of claim 1, wherein the compressible material comprises an elastomer.
 4. The method of claim 1, wherein the embossable layer comprises a deformable solid.
 5. The method of claim 1, wherein the stamper is used to imprint the embossable layer for production of a magnetic recording disk.
 6. The method of claim 3, wherein the stamper is used to imprint the embossable layer for production of a magnetic recording disk.
 7. The method of claim 1, wherein imprinting comprises applying a pressure to the back plane layer in an approximate range of 10 to 2,000 psi.
 8. The method of claim 1, wherein the stamper is used to imprint the embossable layer for production of an optical recording disk.
 9. The method of claim 1, wherein the stamper is used to imprint the embossable layer for production of a display.
 10. The method of claim 1, wherein the stamper is used to imprint the embossable layer for production of a semiconductor device.
 11. The method of claim 1, wherein the embossable layer is imprinted with a feature having a lateral dimension less than approximately 100 nm.
 12. A method of manufacturing a stamper, comprising: generating a patterned layer having a back plane, the patterned layer comprising a hard material; and directly bonding a compressible material on the back plane of the patterned layer.
 13. The method of claim 12, wherein the hard material comprises a rigid material.
 14. The method of claim 12, further comprising curing the compressible material.
 15. The method of claim 12, wherein generating a patterned layer comprises electroplating a master with a metal.
 16. The method of claim 12, further comprising: disposing a masking layer on the back plane of the patterned layer; forming an outer wall on the back plane around the masking layer; removing the masking layer; and disposing the compressible material on the back plane within the outer wall.
 17. The method of claim 15, further comprising curing the compressible material after the compressible material is disposed on the back plane.
 18. The method of claim 17, wherein curing is performed at a temperature approximately in a range of room temperature to 150 degrees C.
 19. The method of claim 12, further comprising: forming an outer wall around the patterned layer to form a cavity above the back plane of the patterned layer; and disposing the compressible material on the back plane of the patterned layer within the outer wall.
 20. The method of claim 19, further comprising curing the compressible material.
 21. The method of claim 12, wherein the hard material has a hardness value in approximately a range of HV100 to HV1000.
 22. The method of claim 12, wherein the compressible material has a hardness value in approximately a range of 20 to 25 Shore 00 scale.
 23. The method of claim 12, wherein the compressible material has a hardness value in approximately a range of 10 to 100 Shore A scale. 